The goal of this research is to develop a quantitative strategy for systematically monitoring the abundance and modifications of postsynaptic proteins. The postsynaptic density (PSD) is a specialized membrane structure essential for neuronal communication. Dynamic protein changes in the PSD play a pivotal role in synapse plasticity. Dysregulation of PSD proteins has been implicated in the etiology of a variety of neurological disorders, such as depression, epilepsy, substance abuse and neurodegeneration. Approximately 1,000 proteins including neurotransmitter receptors and regulatory proteins have been identified in the PSD, but a quantitative, dynamic view of the protein components is still missing. Much less is known about the modulation of posttranslational modifications (e.g. phosphorylation) in the PSD. The main challenge is how to consistently quantify the PSD proteins and their functional modifications under different physiological and pathological conditions. We hypothesize that targeted proteomics will provide a simple, large-scale, and sensitive measurement of proteins and modifications in the PSD. Targeted proteomics uses a specific mass spectrometry technology termed Selected Reaction Monitoring (SRM) or Multiple Reaction Monitoring (MRM). The targeted proteomics overcomes a number of caveats associated with conventional discovery mass spectrometry, such as limited reproducibility, data redundancy and compromised sensitivity. We will first obtain comprehensive PSD datasets and then develop an SRM-based strategy to quantify core PSD proteins, as well as associated phosphorylation events. The strategy will be thoroughly tested to profile PSD components in a cellular model of synaptic activation and during the development of Huntington disease. The study will establish an SRM-based strategy for targeted quantitative PSD analysis. The strategy is expected to greatly simplify current proteomics platform, and will provide crucial basis for understanding molecular mechanisms of learning, memory and neurodegeneration. PUBLIC HEALTH RELEVANCE: Molecular regulation of synapse is the key to the formation of learning and memory. We propose to develop a simplified state-of-the-art mass spectrometry technology to quantitatively monitor the dynamics of proteins and posttranslational modifications in the postsynaptic compartment. The methods will provide a generic approach for investigating the synaptic plasticity under diverse physiological and pathological conditions.